JP7029313B2 - Manufacturing method of metal ultrafine powder - Google Patents

Description

The present invention relates to a method for producing ultrafine metal powder.

When producing ultrafine metal powder, a vapor phase chemical reaction method using a CVD (Chemical Vapor Deposition) device (hereinafter, also simply referred to as “CVD method”) is common. On the other hand, the applicant of the present application forms a high-temperature reducing flame in the furnace using a burner, and heats, evaporates, and reduces the metal compound in the flame to have a particle size larger than that of the raw material metal compound. We are proposing a technology for producing small metal ultrafine powder. Compared with the CVD method, this method does not use chloride as a raw material and the heating method is direct heating by a flame, so that submicron metal ultrafine powder can be safely produced at low cost.

By the way, in recent years, with the progress of miniaturization of electronic parts used for mobile terminals and the like, there are various needs for metal powders used for these electronic parts, and the particle size and particle size distribution of the metal ultrafine powder and the particle size distribution There are various types of shapes depending on the application.

Some metal ultrafine powders used in the above electronic components are required to have a narrow particle size distribution. For example, when the particle size distribution of nickel ultrafine powder used as an internal electrode of a multilayer ceramic capacitor is wide, the expansion / contraction behavior differs due to the difference in particle size of nickel ultrafine powder in the heat treatment step when manufacturing a laminated ceramic capacitor. , There is a high possibility that structural defects such as cracks and delamination will occur.
Therefore, as the nickel ultrafine powder used as an internal electrode of a monolithic ceramic capacitor, nickel ultrafine powder having a narrow (sharp) particle size distribution as much as possible is desired.

According to Patent Document 1, nickel ultrafine powder (nickel powder having an average particle size of 0.1 to several μm) is produced and then classified with a liquid cyclone (wet classification treatment) to obtain nickel ultrafine powder having a narrow particle size distribution. A technique for producing fine powder is disclosed.

On the other hand, a wide particle size distribution may be required. For example, when a high packing density is required such as a sealing material for a semiconductor chip or a material for a lithium battery, a wide particle size distribution is preferable because the filling rate is improved by mixing large particles and small particles.

Patent Document 2 discloses that an electrode made of carbon particles obtained by mixing 10 to 35 wt% of particles having an average particle size of 0.8 μm and 90 to 65 wt% of particles having an average particle size of 3 μm is used as a lithium occlusion negative electrode. ing.

Japanese Unexamined Patent Publication No. 2001-073007 Japanese Unexamined Patent Publication No. 04-0821172

However, in the method described in Patent Document 1, the nickel ultrafine powder production step and the nickel ultrafine powder classification step are performed as separate steps, and it is necessary to separately provide equipment, so that the manufacturing cost increases. There was a problem that productivity was lowered.

Further, in Patent Document 1, since a wet classification method is used, there is a possibility that the nickel ultrafine powder dried after classifying the nickel ultrafine powder may be accompanied by strong aggregation, and the handleability when manufacturing a monolithic ceramic capacitor deteriorates. There was a problem of doing it.

Further, in the method described in Patent Document 2, a step of producing particles having an average particle size of 0.8 μm, a step of producing particles having an average particle size of 3 μm, and a step of mixing these two particles are performed in different steps. Therefore, there is a problem that the manufacturing method of the lithium occlusion negative electrode becomes complicated.

The present invention has been made in view of the above circumstances, and avoids problems such as aggregation that adversely affect the handling property of the ultrafine metal powder, and is easily desired in the particle manufacturing process instead of a separate process. An object of the present invention is to provide a method for producing a metal ultrafine powder capable of producing a metal ultrafine powder having a particle size distribution.

In order to solve the above problems, the present invention has the following configurations.
[1] A reduction flame is formed by burning fuel with a burner using oxygen or oxygen-enriched air as a combustion-supporting gas in a cylindrical furnace that is shielded from the outside air, and powdery into the reduction flame. A method for producing metal ultrafine powder, which produces metal ultrafine powder by supplying a raw material powder which is a metal or a metal compound and heating, evaporating, and reducing the raw material powder.
In the furnace, a swirling flow for cooling the heating, the evaporation, and the reduced raw material powder is formed, and the strength of the swirling flow is adjusted to obtain the desired particle size distribution. A method for producing ultrafine metal powder that produces fine powder.
[2] The metal super fine according to [1], wherein the S value defining the strength of the swirling flow is represented by the following formula (1), and the particle size distribution of the metal ultrafine powder is controlled by changing the S value. How to make fine powder.
S = (Fs / Fz) / (D / d) ... (1)
However, in the above formula (1),
Fs: Momentum of swirling gas in the furnace,
Fz: Burner eruption gas momentum,
D: furnace inner diameter,
d: Burner outlet diameter, respectively.
[3] The method for producing metal ultrafine powder according to [2], wherein the S value is adjusted by the amount of the inert gas ejected from the side wall of the furnace in the tangential direction of the furnace.
[4] The burner is placed at the top of the furnace and
The raw material powder is supplied to the burner,
In the upper part of the furnace, the raw material powder is heated, evaporated, and reduced.
The method for producing a metal ultrafine powder according to any one of [1] to [3], which forms the swirling flow in the lower part of the furnace.

According to the method for producing ultrafine metal powder of the present invention, the raw material powder is heated, evaporated, and reduced in the upper part of the furnace, and then the heated, evaporated, and reduced raw material powder is generated in the same furnace. By cooling with the swirling flow and adjusting the swirling flow intensity (airflow swirling strength), it is possible to generate metal ultrafine powder having a desired particle size distribution.

That is, continuous treatment in the same furnace makes it possible to produce metal ultrafine powder having a desired particle size distribution.
As a result, the metal ultrafine powder having a desired particle size distribution can be easily obtained as compared with the conventional method of producing the metal ultrafine powder at different places and classifying the produced metal ultrafine powder. Can be manufactured.

Further, since the wet classification step is not used, the metal ultrafine powder having a desired particle size distribution is less likely to aggregate, and the handling property of the metal ultrafine powder can be improved.

In the present specification, the metal ultrafine powder means a metal powder having an average particle size of less than 1 μm.
The average particle size of the metal ultrafine powder means the average primary particle size. Specifically, the average particle size of the metal ultrafine powder is image data obtained by observing 20 different places at a magnification of 20000 times using FE-SEM (JSM-6700F (manufactured by JEOL Ltd.)). Is a value obtained by analyzing using image analysis software (“Scandium”; manufactured by Soft Imaging System GmbH).

It is a schematic diagram which shows the schematic structure of the metal ultrafine powder production apparatus used when performing the metal ultrafine powder production method which concerns on one Embodiment of this invention. It is a top view of the tip of the burner shown in FIG. It is a figure which shows the BB line cross section of the tip of the burner shown in FIG. It is a figure which shows the AA line cross section of the furnace and the inert gas supply part shown in FIG. It is a photograph taken by FE-SEM of the nickel ultrafine powder recovered from the bag filter when the S value which defines the strength of the swirling flow is 8.1. It is a photograph taken by FE-SEM of nickel ultrafine powder recovered from a bag filter when the S value which defines the strength of a swirling flow is 1.0. It is a photograph taken by FE-SEM of nickel ultrafine powder recovered from a bag filter when the S value which defines the strength of a swirling flow is 0.4. It is a figure which shows the transition of the value of Cv / Cv ₀ when the S value which defines the strength of a swirl flow is changed.

Hereinafter, an embodiment to which the present invention is applied will be described in detail with reference to the drawings. The drawings used in the following description are for explaining the configuration of the embodiment of the present invention, and the sizes, thicknesses, dimensions, etc. of the illustrated parts are related to the dimensions of the actual metal ultrafine powder manufacturing apparatus. May be different.

FIG. 1 is a schematic diagram showing a schematic configuration of a metal ultrafine powder production apparatus used when performing the method for producing metal ultrafine powder according to an embodiment of the present invention. In FIG. 1, the Y direction indicates the extending direction (vertical direction) of the furnace 17, and the X direction indicates a plane direction orthogonal to the Y direction.
In the present embodiment, the "metal ultrafine powder" means a metal powder having an average particle size of less than 1 μm.

(Metal ultrafine powder manufacturing equipment)
First, with reference to FIG. 1, the configuration of the metal ultrafine powder manufacturing apparatus 10 used when performing the method for producing the metal ultrafine powder of the present embodiment will be described.
The metal ultrafine powder manufacturing apparatus 10 includes a fuel gas supply source 11, a raw material feeder 12, a burner 13, a combustible gas supply source 15, a furnace 17, a plurality of inert gas supply units 18, and an inert gas. It has a supply source 19, a bag filter 21, and a blower 22.

The fuel gas supply source 11 is connected to the raw material feeder 12. The fuel gas supplied from the fuel gas supply source 11 is supplied to the burner 13 together with the raw material powder supplied from the raw material feeder 12. The fuel gas also functions as a carrier gas for transporting the raw material powder. As the fuel gas, for example, natural gas, propane, or the like can be used.

The raw material feeder 12 is connected to the fuel gas supply source 11 and the burner 13. The raw material feeder 12 supplies the raw material powder to the burner 13.
The raw material powder includes, for example, metal particles such as nickel, cobalt, copper, silver and iron, metal oxides (metal oxides) such as nickel, cobalt, copper, silver and iron, and nickel, cobalt and copper. , Particles of metal compounds such as hydroxides of metals such as silver and iron can be used.

The burner 13 is arranged at the top (upper end) of the furnace 17 so that the extending direction of the burner 13 coincides with the Y direction. The tip of the burner 13 forming the reduction flame is housed in the upper end of the furnace 17. As a result, the burner 13 forms a reducing flame in the upper part of the furnace 17.

FIG. 2 is a plan view of the tip of the burner shown in FIG. 1, and FIG. 3 is a view showing a cross section of the tip of the burner shown in FIG. 2 along the line BB.

As shown in FIGS. 2 and 3, the burner (sometimes referred to as a “burner nozzle”) 13 includes a raw material supply pipe 31, a raw material supply path 32, a plurality of raw material ejection holes 34, and a primary fuel-supporting gas supply pipe. 36, a primary fuel-supporting gas supply path 37, a plurality of primary fuel-supporting gas ejection holes 39, a cooling jacket pipe 42, a secondary fuel-supporting gas supply path 43, and a plurality of secondary fuel-supporting gases. It has a ejection hole 45 and.

The raw material supply pipe 31 extends in the axial direction of the burner 13 and is arranged at the center of the burner 13. The central axis of the raw material supply pipe 31 coincides with the central axis 13A of the burner 13.
The raw material supply path 32 is a space provided inside the raw material supply pipe 31, and extends in the axial direction of the burner 13. The raw material supply path 32 is connected to the raw material feeder 12.
The raw material supply path 32 transports the raw material powder and the carrier gas (including the fuel gas) to the tip end side of the burner 13. As the carrier gas, a fuel gas alone or a mixed gas of the fuel gas and an inert gas (for example, nitrogen, argon, etc.) supplied from a supply facility (not shown) can be used.

The plurality of raw material ejection holes 34 are provided so as to penetrate the end portion of the raw material supply pipe 31 (the end portion on the side where the reduction flame is formed). The plurality of raw material ejection holes 34 are arranged radially on the same circumference with respect to the central axis 13A of the burner 13 at equal intervals. The plurality of raw material ejection holes 34 can be provided so as to be inclined outward at, for example, 15 to 50 ° C. with respect to the central axis 13A of the burner 13.

The primary fuel-supporting gas supply pipe 36 extends in the axial direction of the burner 13, and accommodates the raw material supply pipe 31 inside the burner 13. The central axis of the primary fuel-supporting gas supply pipe 36 coincides with the central axis 13A of the burner 13. The primary flammable gas supply pipe 36 has a ring-shaped protrusion 36A inside. The protrusion 36A is in contact with the outer surface of the raw material supply pipe 31.

The primary flammable gas supply pipe 36 has a front plate portion 36B arranged on the tip end side of the burner 13. The front plate portion 36B is arranged so as to project from the tip surface 31a of the raw material supply pipe 31. Further, the inner wall of the front plate portion 36B is an inclined surface whose opening diameter becomes smaller toward the tip surface 31a of the raw material supply pipe 31 from the tip of the front plate portion 36B.
As a result, a combustion chamber C, which is a mortar-shaped space, is formed on the tip surface 31a side of the raw material supply pipe 31.

The primary fuel-supporting gas supply path 37 is an annular space formed between the raw material supply pipe 31 and the primary fuel-supporting gas supply pipe 36. The primary combustible gas supply path 37 is connected to the combustible gas supply source 15. The primary combustible gas supply path 37 transports the primary combustible gas (eg, oxygen or oxygen-enriched air) supplied from the combustible gas supply source 15.

The plurality of primary combustible gas ejection holes 39 are provided so as to penetrate the protrusions 36A, and are arranged at equal intervals on the circumference. The center of the circle passing through the plurality of primary combustible gas ejection holes 39 coincides with the central axis 13A of the burner 13.
The plurality of primary combustible gas ejection holes 39 eject the primary combustible gas transported by the primary combustible gas supply path 37 in parallel with the central axis 13A of the burner 13.

The cooling jacket pipe 42 has a cylindrical shape, and is provided on the outside of the primary fuel-supporting gas supply pipe 36 so as to accommodate the primary fuel-supporting gas supply pipe 36. The central axis of the cooling jacket tube 42 coincides with the central axis 13A of the burner 13.
The cooling jacket pipe 42 has a double pipe structure through which cooling water can flow. As a result, the cooling jacket tube 42 cools the burner 13 with the cooling water.

The secondary fuel-supporting gas supply path 43 is an annular space formed between the primary fuel-supporting gas supply pipe 36 and the cooling jacket pipe 42. The secondary flammable gas supply path 43 is connected to the flammable gas supply source 15. The secondary combustion-supporting gas supply path 43 transports the secondary combustion-supporting gas (for example, oxygen or oxygen-enriched air) supplied from the combustion-supporting gas supply source 15 to the combustion chamber C side.

The plurality of secondary combustion-supporting gas ejection holes 45 are provided so as to penetrate the front plate portion 36B. The plurality of secondary flammable gas ejection holes 45 are arranged at equal intervals on the circumference in a plan view.
The center of the circle passing through the plurality of secondary combustion-supporting gas ejection holes 45 coincides with the central axis 13A of the burner 13. The plurality of secondary flammable gas ejection holes 45 are all arranged so as to be inclined so that the injection direction thereof is toward the central axis 13A of the burner 13.
The plurality of secondary combustible gas ejection holes 45 inject the secondary combustible gas transported to the secondary combustible gas supply path 43 toward the combustion chamber C.

The burner 13 having the above configuration forms a flame by burning the fuel gas using oxygen or oxygen-enriched air as a combustion-supporting gas. At this time, by supplying a smaller amount of oxygen (fuel-supporting gas) than the amount of oxygen that completely burns the fuel gas, a reducing flame in which hydrogen and carbon monoxide remain in the flame (hereinafter, simply "reducing flame"). ") Can be formed.

As shown in FIG. 1, the combustible gas supply source 15 is connected to the burner 13 (specifically, the primary combustible gas supply path 37 and the secondary combustible gas supply path 43 shown in FIG. 3). ing. The combustion-supporting gas supply source 15 supplies the primary combustion-supporting gas to the primary combustion-supporting gas supply path 37, and supplies the secondary combustion-supporting gas to the secondary combustion-supporting gas supply path 43.

FIG. 4 is a diagram showing a cross section of the furnace and the inert gas supply unit shown in FIG. 1 along line AA. In FIG. 4, the same components as those of the structure shown in FIG. 1 are designated by the same reference numerals.

As shown in FIGS. 1 and 4, the furnace 17 has a cylindrical shape and extends in the vertical direction. The cut surface of the furnace 17 in the X direction (cross section when cut along the AA line) is a perfect circle. The inside of the furnace 17 is isolated from the outside air.
A burner 13 is attached to the top (upper end) of the furnace 17 so that the tip of the burner 13 faces downward. Further, a water cooling structure (for example, a water cooling jacket) (for example, a water cooling jacket) (not shown) is provided on the side wall 17A of the furnace 17. The inner diameter D in the furnace 17 can be, for example, 0.8 m.

The upper portion 17-1 in the furnace 17 is used as a growth region for the metal ultrafine powder. That is, in the upper portion 17-1 in the furnace 17, the metal or the metal compound which is the raw material powder is heated, evaporated, and reduced.

On the other hand, in the lower portion 17-2 in the furnace 17, the heated, evaporated, and reduced raw material powder is exposed to the swirling flow E to generate metal ultrafine powder having a desired particle size distribution. ..

In the lower portion 17-2 of the furnace 17, a portion of the lower portion 17-2 located below the arrangement region of the plurality of inert gas supply portions 18, is a mixture of gas (specifically, combustion exhaust gas and inert gas) from the furnace 17. A take-out port 17B is provided for taking out (gas, etc.) and metal ultrafine particles having a desired particle size distribution.

As shown in FIGS. 1 and 4, the plurality of inert gas supply units 18 (for example, ports) are provided on the side wall 17A of the furnace 17 and project from the outer surface 17a of the side wall 17A of the furnace 17.
The plurality of inert gas supply units 18 are arranged in the circumferential direction of the side wall 17A of the furnace 17 and in the extending direction (vertical direction) of the furnace 17.
The plurality of inert gas supply units 18 are connected to the inert gas supply source 19, and the inert gas (for example, nitrogen) supplied from the inert gas supply source 19 is ejected into the furnace 17.

As shown in FIG. 4, the plurality of inert gas supply units 18 are arranged so that the extending direction thereof is the same as the tangential direction of the side wall 17A of the furnace 17. As a result, the inert gas ejected into the furnace 17 makes it possible to form a uniform swirling flow E in the furnace 17.

By this swirling flow E, the raw material powder heated, evaporated, and reduced in the upper portion 17-1 of the furnace 17 is exposed to generate metal ultrafine powder having a desired particle size distribution, and the desired particle size distribution can be obtained. The metal ultrafine powder is transported together with the gas to the bag filter 21 via the take-out port 17B.
Further, the strength of the swirling flow E needs to be appropriately adjusted depending on what kind of particle size distribution of the metal ultrafine powder is to be obtained. The strength of the swirling flow E is the amount of the inert gas ejected from the inert gas supply unit 18 (in other words, the amount of the inert gas ejected from the side wall 17A of the reactor 17 in the tangential direction of the reactor 17). It can be adjusted by changing it.

Specifically, the strength of the swirling flow E is adjusted by controlling the S value that defines the strength of the swirling flow E (the swirling strength of the air flow) in the furnace 17 represented by the following equation (1).
S = (Fs / Fz) / (D / d) ... (1)
However, in the above equation (1), "Fs" is the momentum of the swirling gas (inert gas etc. ejected from the inert gas supply unit 18) in the furnace 17, and "Fz" is the gas ejected from the burner 13. The momentum of (carrier gas or the like ejecting the raw material from the raw material ejection hole 34 of the burner 13), “D” indicates the inner diameter of the furnace 17, and “d” indicates the outlet diameter of the burner 13.

In the above formula (1), the S value that defines the strength of the swirling flow E is preferably a value larger than 1.0 (see FIG. 8 to be described later). When the S value that defines the strength of the swirling flow E is 1.0 or less, the metal ultrafine powder generated in the furnace 17 contains many connecting particles, so that a spherical ultrafine powder is required. It is not suitable for the field of electronic parts.

In the present embodiment, in order to obtain a narrow (sharp) particle size distribution, it is necessary to perform an operation so that the S value becomes small. However, when S <1.0, a large number of connected particles are generated (see FIG. 8). Further, in order to obtain a wide particle size distribution, it is necessary to perform an operation such as increasing the S value.
Specifically, as the operation of reducing the S value, the operation of reducing the momentum of the swirling gas in the furnace 17 (that is, reducing the amount of the inert gas ejected from the inert gas supply unit 18) or the operation of reducing the amount of the inert gas ejected from the inert gas supply unit 18 is performed. An operation of increasing the momentum of the gas ejected from the burner 13 (that is, increasing the amount of each gas ejected from the burner 13) can be mentioned.

By changing the strength of the swirling flow E in the furnace 17 (the swirling strength of the air flow) in this way, it is possible to control the metal ultrafine powder so as to have a desired particle size distribution.

That is, by heating, evaporating, and reducing the raw material powder in the upper part 17-1 in the furnace 17, and then adjusting the strength of the swirling flow E generated in the lower part in the same furnace (the swirling strength of the airflow). , It becomes possible to produce metal ultrafine powder having a desired particle size distribution.

Therefore, in the same furnace, it is possible to produce metal ultrafine powder having a desired particle size distribution by continuous treatment.
As a result, the metal ultrafine powder having a desired particle size distribution can be easily obtained as compared with the conventional method of producing the metal ultrafine powder at different places and classifying the produced metal ultrafine powder. Can be generated.

Further, since the wet classification step is not used, the metal ultrafine powder having a desired particle size distribution is less likely to aggregate, and the handleability can be improved.

In FIG. 4, as an example, the case where the four inert gas supply units 18 are provided in the circumferential direction of the side wall 17A of the furnace 17 has been described as an example, but it is not arranged in the circumferential direction of the side wall 17A of the furnace 17. The number of the active gas supply units 18 can be appropriately selected as needed, and is not limited to FIG.

Further, in FIG. 1, as an example, the case where the three-stage inert gas supply unit 18 is arranged in the extending direction of the furnace 17 has been described as an example, but the inert gas supply unit 18 in the extending direction of the furnace 17 has been described. The number of stages of 18 is not limited to FIG.

Further, in the present embodiment, as shown in FIG. 4, the case where the port is used as the plurality of inert gas supply units 18 has been described as an example, but the slit is used as the plurality of inert gas supply units 18. May be good.

The bag filter 21 has a gas discharge unit 21A connected to the blower 22 and a metal ultrafine powder recovery unit 21B. The gas discharge unit 21A is provided on the upper part of the bag filter 21. The metal ultrafine dust collecting unit 21B is provided at the lower end of the bag filter 21.
The bag filter 21 is connected to the outlet 17B of the furnace 17. The gas and the metal ultrafine powder having a desired particle size distribution are transported to the bag filter 21 via the take-out port 17B.

The bag filter 21 recovers the metal ultrafine powder having a desired particle size distribution from the metal ultrafine powder recovery unit 21B among the gas transported from the furnace 17 and the metal ultrafine powder having a desired particle size distribution.
The blower 22 sucks the gas in the bag filter 21 through the gas discharge unit 21A and discharges the gas as exhaust gas.

According to the metal ultrafine powder manufacturing apparatus of the present embodiment, the burner 13 is arranged at the top of the furnace 17 and forms a reduction flame in the upper 17-1 in the furnace 17, and is provided in the lower 17-2 of the furnace 17. , A plurality of inert gas supply units 18 for generating a swirling flow E, and the raw material powder is heated, evaporated, and reduced in the upper portion 17-1 in the furnace 17, and then heated, evaporated, and reduced. When the resulting raw material powder is passed through a flow field having a swirling flow E generated in the lower portion 17-2 of the furnace 17, the strength of the swirling flow E (swirl strength of the air flow) is adjusted to obtain a desired particle size. It is possible to produce distributed metal ultrafine powder.

That is, in the present embodiment, it is possible to produce metal ultrafine powder having a desired particle size distribution by continuous treatment in the same furnace 17.
As a result, the particle size distribution can be adjusted not in separate steps such as classification and mixing, but in the process of producing the metal ultrafine powder, so that the metal ultrafine powder having the desired particle size distribution can be easily produced as compared with the conventional method.

Further, since the wet process is not used at the time of classification, the metal ultrafine powder having a desired particle size distribution is less likely to aggregate, and the handleability can be improved.

Further, according to the present invention, it is also possible to obtain metal ultrafine powder containing a large amount of two different particle sizes by one continuous step of producing metal ultrafine powder.

The number and positional relationship (layout) of the raw material ejection holes 34, the primary fuel-supporting gas ejection holes 39, and the secondary combustion-supporting gas ejection holes 45 can be appropriately selected, and the raw material ejection holes shown in FIG. 2 can be selected as appropriate. The number and positional relationship (layout) of the holes 34, the primary fuel-supporting gas ejection holes 39, and the secondary combustion-supporting gas ejection holes 45 are not limited.
Further, the ejection angles of the raw material ejection hole 34, the primary combustible gas ejection hole 39, and the secondary combustible gas ejection hole 45 can be appropriately selected.

Further, in the present embodiment, the furnace 17 having a water-cooled structure has been described as an example, but instead, a furnace in which the side wall 17A is made of a refractory material (for example, bricks, amorphous castables, etc.) is used. You may.

(Manufacturing method of ultrafine metal powder)
Next, a method for producing the metal ultrafine powder of the present embodiment will be described with reference to FIGS. 1 and 4.
First, by supplying the fuel gas and the raw material powder (powder made of a metal or a metal compound), the primary fuel-supporting gas and the secondary fuel-supporting gas to the burner 13, the upper portion 17 in the furnace 17 is supplied. A high-temperature reduction flame is formed in -1 with a combustion-supporting gas and a fuel gas, and the raw material powder is heated, evaporated, and reduced in the high-temperature reduction flame.
At this time, a swirling flow E is formed in the lower portion 17-2 of the furnace 17 by ejecting an inert gas (for example, nitrogen) from the tangential direction of the side wall 17A of the furnace 17.

Next, the heated, evaporated, and reduced raw material powder moved to the lower portion 17-2 of the furnace 17 passes through a flow field having a swirling flow E, and the swirling flow E makes the metal super metal having a desired particle size distribution. Fine particles are produced. After that, the metal ultrafine particles having the desired particle size distribution are transported together with the gas to the bag filter 21 via the take-out port 17B of the furnace 17.

In the bag filter 21, the gas and the metal ultrafine particles having a desired particle size distribution are separated, and the metal ultrafine particles having a desired particle size distribution are obtained from the lower end.
This completes the production of ultrafine metal particles having a desired particle size distribution.

According to the method for producing ultrafine metal particles of the present embodiment, the raw material powder is heated, evaporated, and reduced in the upper portion 17-1 in the furnace 17, and then the heated, evaporated, and reduced raw material powder is the same. When passing through a flow field having a swirling flow E generated in the furnace 17, the strength of the swirling flow E (the swirling strength of the air flow) is adjusted to generate metal ultrafine powder having a desired particle size distribution. Is possible.

That is, continuous treatment in the same furnace 17 makes it possible to produce metal ultrafine powder having a desired particle size distribution.
As a result, the particle size distribution can be adjusted not in separate steps such as classification and mixing, but in the process of producing the metal ultrafine powder, so that the metal ultrafine powder having the desired particle size distribution can be easily produced as compared with the conventional method.

Further, since the wet process is not used at the time of classification, the metal ultrafine powder having a desired particle size distribution is less likely to aggregate, and the handling property of the metal ultrafine powder can be improved.

Further, according to the present invention, it is also possible to obtain metal ultrafine powder containing a large amount of two different particle sizes by one continuous step of producing metal ultrafine powder.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such a specific embodiment, and various within the scope of the gist of the present invention described in the claims. Can be transformed / changed.

(Example)
In the examples, first, nickel oxide powder (3 kg / h) having an average particle size of 5 μm was used as the raw material powder, and nickel ultrafine powder was produced by the metal ultrafine powder producing apparatus 10 shown in FIG.
At this time, natural gas (11.1 Nm ³ / h) is used as the fuel gas, and oxygen (oxygen ratio 0.9, distribution ratio between the primary and secondary combustion-supporting gas) is used as the fuel-supporting gas: total oxygen. The amount was distributed so as to be 2: 8), the inner diameter D of the furnace 17 was 0.8 m, and nitrogen (50 to 250 Nm ³ / h) was used as the inert gas.
The above-mentioned "oxygen ratio" refers to a value when the amount of oxygen required for complete combustion of fuel is defined as 1.

Further, as the burner 13 constituting the metal ultrafine powder manufacturing apparatus 10, the burner 13 having the structure shown in FIGS. 2 and 3 was used.
In addition, when producing nickel ultrafine powder, the amount of natural gas supplied, the value of the oxygen ratio, and the amount of nickel oxide supplied are kept constant, and the amount of nitrogen supplied into the furnace 17 is changed to change the swirling strength of the air flow. The strength of the swirling flow E was adjusted by controlling the S value that defines the strength of the swirling flow E).

The metal ultrafine powder produced by the above method was observed at 20 different locations using FE-SEM (JSM-6700F (manufactured by JEOL Ltd.)) at a magnification of 20000 times.
Next, the image data at each of the 20 observed locations was analyzed using image analysis software (“Scandium”; manufactured by Soft Imaging System GmbH), and the Cv value was calculated based on the particle size distribution obtained from this analysis result. And compared.

The Cv value is obtained by the following formula (2). The Cv value is a value indicating the width of the particle size distribution, and the smaller the Cv value, the narrower the particle size distribution (sharp), and the larger the Cv value, the wider the particle size distribution.
Cv value = "standard deviation (μm)" / "average particle size (μm)" x 100 (%) ... (2)
In the above formula (2), the "standard deviation (μm)" and the "average particle size (μm)" are values obtained by using the above image analysis software.

FIG. 5 is a photograph of nickel ultrafine powder recovered from a bag filter taken by FE-SEM when the S value defining the strength of the swirling flow is 8.1. FIG. 6 is a photograph of nickel ultrafine powder recovered from a bag filter taken by FE-SEM when the S value defining the strength of the swirling flow is 1.0.
FIG. 7 is a photograph of nickel ultrafine powder recovered from a bag filter taken by FE-SEM when the S value defining the strength of the swirling flow is 0.4.

As shown in FIGS. 5 to 7, it was confirmed that when the S value defining the strength of the swirling flow E was less than 1.0, a large number of connected particles were present. From this, it was confirmed that the S value defining the strength of the swirling flow E is preferably 1.0 or more from the viewpoint of preventing the connected particles.

FIG. 8 is a diagram showing the transition of the value of Cv / Cv ₀ when the S value defining the strength of the swirling flow is changed. As Cv ₀ , the Cv value when the S value defining the strength of the swirling flow was 4.5 was used.

As shown in FIG. 8, it was confirmed that the particle size distribution of the nickel ultrafine powder can be controlled by changing the S value that defines the strength of the swirling flow.
That is, when the S value is made small, the particle size distribution becomes sharp (the Cv value becomes small). However, if the S value is less than 1.0, a large number of connecting particles are generated, which is not preferable as an internal electrode material, for example. On the other hand, when the S value is increased, the particle size distribution becomes wider and large particles are included.

The present invention is applicable to a method for producing ultrafine metal powder.

10 ... Metal ultrafine powder production equipment, 11 ... Fuel gas supply source, 12 ... Raw material feeder, 13 ... Burner, 13A ... Central axis, 15 ... Combustible gas supply source, 17 ... Furnace, 17a ... Outer surface, 17A ... Side wall, 17B ... Extraction port, 17-1 ... Upper part, 17-2 ... Lower part, 18 ... Inactive gas supply part, 19 ... Inactive gas supply source, 21 ... Bug filter, 21A ... Gas discharge part, 21B ... Metal ultrafine powder recovery Part, 22 ... Blower, 31 ... Raw material supply pipe, 31a ... Tip surface, 32 ... Raw material supply path, 34 ... Raw material ejection hole, 36 ... Primary fuel-supporting gas supply pipe, 36A ... Protruding part, 36B ... Front plate part, 37 ... Primary combustion-supporting gas supply path, 39 ... Primary-supporting gas ejection hole, 42 ... Cooling jacket tube, 43 ... Secondary combustion-supporting gas supply path, 45 ... Secondary combustion-supporting gas ejection hole, C ... Combustion chamber, D ... inner diameter, E ... swirling flow

Claims (3)

A reducing flame is formed by burning fuel with a burner using oxygen or oxygen-enriched air as a combustion-supporting gas in a cylindrical furnace that is shielded from the outside air, and powdered metal or metal is put into the reducing flame. A method for producing metal ultrafine powder, which produces metal ultrafine powder by supplying raw material powder which is a compound and heating, evaporating, and reducing the raw material powder.
A swirling flow for cooling the heating, the evaporation, and the reduced raw material powder is formed in the furnace, and the S value defining the strength of the swirling flow represented by the following formula (1) is changed. A method for producing a metal ultrafine powder, which produces the metal ultrafine powder having a desired particle size distribution by controlling the particle size distribution of the metal ultrafine powder .
S = (Fs / Fz) / (D / d) ... (1)
However, in the above formula (1),
Fs: Momentum of swirling gas in the furnace,
Fz: Burner eruption gas momentum,
D: furnace inner diameter,
d: Burner outlet diameter, respectively. The method for producing an ultrafine metal powder according to claim 1 , wherein the S value is adjusted by the amount of the inert gas ejected from the side wall of the furnace in the tangential direction of the furnace. The burner is located at the top of the furnace and
The raw material powder is supplied to the burner,
In the upper part of the furnace, the raw material powder is heated, evaporated, and reduced.
The method for producing a metal ultrafine powder according to claim 1 or 2 , wherein the swirling flow is formed in the lower part of the furnace.

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